# Velocity inlet boundary conditions

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 October 8, 2008, 07:00 Velocity inlet boundary conditions #1 abm Guest   Posts: n/a Hello I am analysing the flow over an airfoil. But when I'm setting up the problem, this message appears: "WARNING: Velocity inlet boundary conditions are not appropriate for compressible flow problems. Please change the boundary condition types used for this problem" Then I can go on with the analysis, but I don't know what this problem means. Thank you very much

 October 8, 2008, 07:21 Re: Velocity inlet boundary conditions #2 doki Guest   Posts: n/a velocity inlet BC type, should only be used for incompressible flows. if your case is compressible, change it to pressure inlet or ...

 October 8, 2008, 07:49 Re: Velocity inlet boundary conditions #3 abm Guest   Posts: n/a But if I change it to pressure inlet, how can I simulate a 30m/s flow over the airfoil?? Thank you

 October 8, 2008, 07:56 Re: Velocity inlet boundary conditions #4 Rok Sibanc Guest   Posts: n/a Set inlet as mass flow inlet and calculate it as: area * velocity * density

 October 8, 2008, 09:17 Re: Velocity inlet boundary conditions #5 DANG Huixue Guest   Posts: n/a you can define the total pressure as: 0.5 * rho * velocity * velocity, just the same as the dynamic pressure

 October 8, 2008, 10:37 Re: Velocity inlet boundary conditions #6 CL Guest   Posts: n/a Hi abm, Dont use mass flow inlet as ur boundary condition becuase for compressible flow density is not constant, so mass flow will not be constant for compressible flows. With regards, CL

 October 8, 2008, 19:33 Re: Velocity inlet boundary conditions #7 kartik Guest   Posts: n/a Hey You could use Pressure Far field. you can specify the mac number for the velocity you want to provide.

 October 9, 2008, 03:35 Re: Velocity inlet boundary conditions #8 abm Guest   Posts: n/a Thanks to all. Now I have to try all your suggestions, and I'll post the results here. But I think that using mass flow isn't a good idea, as CL said before Thank you very much

 October 9, 2008, 03:59 Re: Velocity inlet boundary conditions #9 doki Guest   Posts: n/a mass flow inlet is of course one of BCs for the compressible flow, but in the case, I think using pressure inlet is more appropriate. pressure far field is something used only for external flow problems, and needs the outer boundaries of the domain to be very far from the inner boundaries. and also it is recommended for M>=0.6 in such cases. by the way, the pressure inlet appears to be more suitable for the case.

 October 25, 2008, 08:51 Re: Velocity inlet boundary conditions #10 abm Guest   Posts: n/a I'm analysing flow around an airfoil near the ground, so I think I can't use pressure far field, and as it's about compressible flow, for me mass inlet is not a good idea. What do you think?

 October 26, 2008, 07:25 Re: Velocity inlet boundary conditions #11 doki Guest   Posts: n/a for the condition, I think you have better use Pressure inlet/outlet conditions. It is a tough problem to encounter, i Know. But sometimes there is no other choices.

 October 26, 2008, 11:11 Re: Velocity inlet boundary conditions #12 abm Guest   Posts: n/a What I don't understand is that, even with this warning, nothing wrong seems to happen, and the results are ok.

 October 27, 2008, 12:39 Re: Velocity inlet boundary conditions #13 doki Guest   Posts: n/a well, yes. there are so many conditions which have the same problem. In many cases there are such conditions in which there is no errors. but when you are doing sth right, then the errors appear!

 October 29, 2008, 05:03 Re: Velocity inlet boundary conditions #14 abm Guest   Posts: n/a The problem happens when I change material density from constant to ideal-gas. I'm trying to prove that the results are ok, instead of this warning

 August 3, 2012, 05:51 velocity inlet in fluent #15 Senior Member   kunar Join Date: Nov 2011 Posts: 117 Rep Power: 7 Dear friends, In fluent, For analysis of 2D naca0012 airfoil velocity inlet we give vcostheta in x component & vsintheta in y component, v is inlet velocity. 1)here i start analysis of 3D wing, for that i take naca 0012 airfoil & extrude 100mm, in gambit and analysis in fluent i have doubt how to set velocity inlet, here i consider my velocity is 50m/s, then what is xyz component,please let me know. 2)if you consider 3D wing, (vtantheta for z component) is correct or wrong, please let me know. 2) how to find angle of attack for 3D wing? please let me know

 July 6, 2014, 05:03 Fluent physics Setup #16 New Member   Wing Boys Join Date: Jul 2014 Posts: 1 Rep Power: 0 We have created the mesh for B-737 wing using ICEM CFD. We have not been able to do the physics setup for fluent. We want to use the following conditions: Mach Number :0.3 We have tried using velocity inlet for inlet conditions, pressure outlet for outlet and pressure farfield for top and bottom surfaces. We have tried to use SST K-omega model but there were divergence detected. PLEASE HELP!!!

 October 18, 2014, 08:52 #17 Member   Michael Kruger Join Date: Jul 2014 Location: South Africa Posts: 38 Rep Power: 4 If you specify pressure inlet as a BC, how do you attain a specified inlet velocity/Mach nr? Also, when simulating flow over an airliner, would gauge total pressure be the ambient pressure at which the plane is flying, and what then would Supersonic/Initial gauge pressure be? __________________ ------------------------------------------------------- Michael

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post mattia Main CFD Forum 0 February 11, 2009 07:06 Ashraf Sharara FLUENT 1 August 21, 2008 07:29 Fernanda Main CFD Forum 3 January 26, 2007 04:09 katy FLUENT 2 January 5, 2006 16:35 M.A. Rakib FLUENT 3 June 7, 2000 09:40

All times are GMT -4. The time now is 19:08.

 Contact Us - CFD Online - Top